Santa Cruz >> Four men injured in two butane hash oil explosions are still recovering from burns suffered in September and October, according to Santa Cruz police.

All the men are out of the hospital, said Santa Cruz Deputy Police Chief Steve Clark.

"Each of the burn victims is undergoing extensive medical treatment as they have severe injuries that will likely have permanent consequences," Clark said Thursday.

None of the men have been arrested, but police plan to send the cases to the Santa Cruz County District Attorney's Office. Prosecutors then will decide whether charges will be filed.

The trouble started Sept. 29 at a garage on the 700 block of Third Street in Santa Cruz.

One way to make hash oil — which is a concentrated, gooey form of marijuana also known as "dabs" — is to put marijuana stems and other parts in a hot water bath while butane is cooked through it. The result is a potent goo that can be smoked on its own or with regular marijuana.

Homemade hash oil contraptions can be dangerous because the butane can escape and find an ignition source, causing an explosion, Santa Cruz police and firefighters said.

In the Third Street fire, butane escaped from the contraption and hit a pilot light on a water heater in a garage. The blast and fire burned a 23-year-old man and 25-year-old man who live at the home, as well as a 23-year-old man who lives elsewhere in Santa Cruz, police said.

The fire blew out at least one window of a neighboring apartment, scorched its balconies and damaged a Volkswagen bus and a Ford Mustang parked near the garage.

Authorities have not named the other men injured in hash oil blasts because they have not been charged.

The second hash oil fire in Santa Cruz this fall took place Oct. 9 on the 100 block of Walk Circle in Santa Cruz. Police said a 29-year-old man was making butane hash oil when he lit a cigarette lighter and it exploded. He suffered burns over 40 percent of his body.

Santa Cruz police have said that hash oil manufacturing in fall 2013 may have been linked to preserving excess marijuana from the fall harvest — similar to canning fruit. Its manufacture in homes and garages is part of a national trend, according to the U.S. Department of Homeland Security.

Butane is colorless and odorless, and neighbors might not be able to smell a hash oil lab next door. However, Santa Cruz police have said that residents can watch for large deliveries of butane canisters.